IE69391B1

IE69391B1 - Fish parasite control

Info

Publication number: IE69391B1
Application number: IE922769A
Authority: IE
Inventors: Jan M Thomassen; Lekang Odd Ivar
Original assignee: Eka Nobel Ab
Priority date: 1991-10-24
Filing date: 1992-10-23
Publication date: 1996-09-18
Also published as: DK89692D0; NO178013B; IE922769A1; SE9103113L; SE468699B; GB2260703A; CA2081218A1; DK169534B1; SE9103113D0; NO178013C; GB2260703B; GB9221942D0; NO922500L; US5313911A; NO922500D0; DK89692A; CA2081218C

Abstract

Parasites on fish are controlled with an aqueous solution containing more than 1.2 but less than 5g, preferably less than 2.9 g, H2O2 per litre.

Description

FISH PARASITE CONTROL The present invention relates to the controlling of parasites on fish.

In connection with fish breeding, parasites cause 5 major problems if not efficiently controlled. Salmon breeding generally meets with problems occasioned by salmon louse (Lepeophtheirus salmonis), a small crustacean which can attach to the fish. If the salmon lice are not controlled, the output and hence the economic yield of the fish breeding will drop. Usually, salmon lice are controlled with different organophosphates, such as dichlorovos or trichlorophon, which are acetylcholinesterase-inhibiting substances. Thus, they are toxic both to fish and to man, and also are not considered environmentally-friendly. Nor are these agents effective against salmon lice in the fry state, but only against adult and half-grown salmon lice. Salmon lice resistant to the agents employed have also been encountered.

JP Published Patent Application 89-317346 discloses the use of hydrogen peroxide for killing parasites on certain fish species. For optimum results, contents of from 400 to 1000 ppm hydrogen peroxide are recommended for use during a time of from l to 20 min.

It has however been found that this treatment is not effective on salmon lice.

The object of the invention is to provide an environmentally-friendly method which is efficacious in connection with fish breeding- for destroying salmon lice and which should not endanger the life of salmon in a fish breeding facility or cause any major harm to the salmon.

The invention provides in one aspect a method for preparing an agent for controlling parasites in fish breeding, said agent being prepared by supplying water in a fish breeding facility, the water having a temperature of 0 to 14°C, with hydrogen peroxide or a -2hydrogen-peroxide-producing substance, so that the H202-content in the water is above 1.2 but below 2.9 g per litre.

In a second aspect, this invention provides a * method for preparing an agent for controlling parasites in fish breeding, said agent being prepared · by supplying water in a fish breeding facility, the water having a temperature of 0 to 14°C, with hydrogen peroxide or a hydrogen-peroxide-producing substance, such that the H202-content in the water is above 1.2 but below 5 g per litre and that this content is maintained within this range for more than 20 min.

Finally, in a third aspect, this invention specifically provides a method for preparing an agent for controlling salmon lice (Lepeophtheirus salmonis) in fish breeding, said agent being prepared by supplying water in a fish breeding facility, the water having a temperature of 0 to 14°C, with hydrogen peroxide or a hydrogen-peroxide-producing substance, such that the H202-content in the water is above 1.2 but below 5 g per litre.

In general, the H2O2 content of water is such that an aqueous solution containing more than 1.2, preferably more .than 1.3, particularly more than 1.4 g H2O2 per litre exists. Suitably, the H20,-content is below 2.9, preferably below 2.7 g per litre. Further, the aqueous solution may contain from 20 to 40, preferably from 27 to 35 parts per thousand salts based on the weight, which salts may have substantially the same composition as in sea-water, i.e. consist of from 70 to 90% by weight of NaCl, the balance substantially being MgCl2, MgSO4, CaSO4, K2SO4, CaCO3 and MgBr2. The * aqueous solution has a temperature of from 0 to 14°C in order to avoid killing of the fish.

The method of this invention is applicable to the controlling of parasites, preferably salmon lice, in the breeding of fish, the fish being preferably from -3the salmon family: Preferably, the H2O2 and salt additions mentioned above are made so that the H202-content is maintained within the above-mentioned ranges at least for a time exceeding 20 min.

Preferably, the hydrogen peroxide content is maintained within the above-mentioned ranges for a time up to between 20 and 60 min, more preferably for a time up to between 20 and 30 min. Suitably, a certain volume of water containing fish and parasites is screened off, so that the exchange with the surrounding water is essentially stopped, whereupon the screened-off water is supplied with a suitable amount of hydrogen peroxide. The water volume may be, for instance, from 10 to 2000 m3, preferably from 200 to 1600 m3, and contain, for instance, from 1 to 100 tonnes of fish.

The water can be screened off by enclosing a fishholding string bag with a substantially waterimpermeable cover, for instance a plastic tarpaulin, so as to form a bag which encloses the fish and the parasites, and which preferably is open only above the water surface. It is also preferred that the volume of the string bag be reduced by lifting its bottom and/or moving its walls together. Preferably, the hydrogen peroxide is supplied during as short a time as possible, without the concentration gradients becoming too high, e.g. during a time of from 2 to 10 min, depending on the water volume, in such an amount that a suitable H202-content is maintained for a suitable time, i.e. at least 20 min. After this time, the water30 impermeable cover is removed so that the water exchange with the surroundings is resumed and the hydrogen peroxide is rapidly diluted. Since it has proved essential that the concentration gradients of the hydrogen peroxide in the water be minimised, the hydrogen peroxide should be supplied to the water by a substantially uniform distribution. According to a -4preferred method, the hydrogen peroxide is added in the form of an aqueous solution through a pipe or a hose having a plurality of nozzles disposed below the water surface, the tube or hose preferably being in the form r· of a closed, substantially horizontal annulus disposed below the water surface. Such an annulus can be * provided by connecting a hose or a pipe to a T-branch connection, in turn connected to a source of hydrogen peroxide, for instance a supply tank. The annulus may for instance have a diameter of from 1 to 6 m, preferably from 2 to 5 m, and have from 10 to 100, preferably from 30 to 70 holes serving as nozzles. It is also preferred that the hydrogen peroxide be supplied in the form of an aqueous solution containing from 10 to 70% by weight of H202, especially from 25 to 55% by weight of H202. To ensure a suitable H202-content in the water for a sufficient period of time, it is preferred that' this content is measured by a method conformed to field analysis. A preferred such method of analysis comprises the steps of supplying a number of vessels, e.g. test tubes or flasks, with the same amount of water, each vessel containing different predetermined amounts of reagent for H202, e.g. KMnO4, thus making it possible to estimate the H202-content of the water.

It has been found that a treatment time above 20 min is required for killing salmon lice to an adequate extent, even if the H202-content is high. It has also been found that treatment times exceeding 60 min are harmful to the fishes in the breeding facility, even if the H202-content is low. Further, it has been found that treatment at too high water temperature is harmful * to the fish, for which reason the temperature is I*· within the range from 0 to 14°C. Preferably, the parasites are destroyed in that the fishes and the parasites are enclosed, together with the water in -5which they live, in a bag and are subjected to hydrogen peroxide, as described in connection with the method of preparing the agent according to the invention. The treatment is ended by removing the bag, so that the water with hydrogen peroxide is diluted with the surrounding water.

Fig. 1 shows an example of how the water in a fish breeding plant can be supplied with hydrogen peroxide, and Fig. 2 shows the dependency of the degree of delousing on the hydrogen peroxide content of the water.

Fig. 1 shows how the fishes 3 in the breeding plant are enclosed by a string bag 1, around which there is disposed an external, substantially water15 impermeable plastic tarpaulin 2 forming a bag which is open only above the water surface. Hydrogen peroxide solution is supplied from a tank 6 on a boat 7 through an annular plastic hose 4 disposed below the water surface and having holes 5 serving as nozzles. -6The invention will now be illustrated by the following Example which, however, is not intended to restrict the invention. Unless otherwise indicated, all contents are given in parts by weight.

EXAMPLE: Destruction of salmon lice with hydrogen peroxide of different concentrations was carried out in a fish breeding facility in the North Sea according to the following description. The water temperature was between 6 and 14C.

Tests 1-3 were performed in small string bags (3x3x3 m) containing 100 salmon weighing 1-2 kg. The bottom of the string bags was pulled up to· a depth of 1-1.5 m, and a plastic tarpaulin was passed underneath and around the string bag so as to form a salmon-hold ing bag, to which a 35% hydrogen peroxide solution was supplied. After 20 min, the tarpaulin was removed, except in Tests 3.1 and 3.2, where this was done after 120 and 60 min, respectively. In Tests 1.1 and 1.2, the hydrogen peroxide content of the water was calculated on the basis of the amount supplied, while the content in the other tests was determined by iodometric titration. Before and after each treatment, the number of lice was counted on 5-10 fishes and the degree of delousing was calculated.

Tests 4, 5,6 and 7 were performed in string bags having a circumference of 40 m, the bottom of the string bags was pulled up to a depth of about 2-3 m, and the bags were provided with an external plastic tarpaulin. In Tests 4, 6 and 7, each string bag contained about 2000 salmon weighing 0.5-1 kg, while the string bag in Test 5 contained about 1500-2000 rainbow trout weighing 1.5-2.5 kg. In Tests 4 and 5, 35% hydrogen peroxide was pumped out into the bag after dilution with equal parts of sea-water. In Tests 6 and 7, 35% hydrogen peroxide was pumped out into the bag through an annular hose system, as shown in Fig. 1. In all the cases, the hydrogen peroxide was supplied in less than about 5 min, and the tarpaulin was removed 20 min after the hydrogen peroxide supply had been ended. The hydrogen peroxide content of the water was determined by iodometric -Ίtitration. The amount of lice was counted on 6-12 fishes before and after the treatment.

The results of all the tests appear from the Table below. The number of salmon lice before and after each treatment is given as the mean value for the examined fishes. The degree of delousing X in per cent in relation to the hydrogen peroxide content of the water is also graphically represented in Fig. 2.

Test No. Amount 35% h2o2 (1) Content H2O2 g/1 Number of salmon lice Delousing degree (%) before after 1.1 90 3.5-5 21 0 100 1.2 30 1.5-2 29 0 100 15 2.1 30 2.7 78 5 94 2.2 15 1.0 52 9 83 3.1 7.5 0.42 87 78 10 3.2 10 0.7 84 32 38 3.3 20 1.34 92 14 85 20 4 400 0.6 19.6 10.2 48 5 760 1.4 51‘ 2.6 95 6 760 0.8 122 49 60 7 760 0.95 131 33 75 25 The results show that the effect of the treatment is considerably enhanced when the hydrogen peroxide content is raised from 1 to 1.5 g per litre, which must be considered most surprising.

Claims

CLAIMS:

1. Method for preparing an agent for controlling parasites in fish breeding, said agent being prepared by supplying water in a· fish breeding facility, the water having a temperature of 0 to 14°C, with hydrogen peroxide or a hydrogen-peroxide-producing substance, so that the H 2 0 2 -content in the water is above 1.2 but below 2.9 g per litre.

2. Method for preparing an agent for controlling parasites in fish breeding, said agent being prepared by supplying water in a fish breeding facility, the water having a temperature of 0 to 14°C, with hydrogen peroxide or a hydrogen-peroxide-producing substance, such that the H 2 0 2 -content in the water is above 1.2 but below 5 g per ‘litre and such that this content is maintained within this range for more than 20 min.

3. Method for preparing an agent for controlling salmon lice (Lepeophtheirus salmonis) in fish breeding, said agent being prepared by supplying water in a fish breeding facility, the water having a temperature of 0 to 14°C, with hydrogen peroxide or a hydrogen-peroxide-producing substance, such that the H 2 0 2 -content in the water is above 1.2 but below 5 g per litre.

4. Method as claimed in any one of claims 2 or 3, wherein the H 2 0 2 -content in the aqueous solution exceeds 1.3 H 2 O 2 g per litre.

5. Method as claimed in claim 1 or 3, wherein the H 2 0 2 -content in the water is maintained within the stated range for more than 20 min.

6. parasites described

7. breeding, preceding A method for preparing an agent for controlling A in fish breeding, substantially as hereinbefore and exemplified. i An agent for controlling parasites in fish whenever prepared by a method claimed in a claim.